Dysfunction of serotoninergic (5HT) systems in the brain have been implicated in neurological and psychiatric conditions. Drugs that interact with brain 5HT 1A receptors are effective in relieving anxiety disorders. LSD and other hallucinogenic drugs have been shown to produce their psychoactive effects through stimulation of brain 5HT2 receptors. 5HT3 receptor antagonists are effective in controlling nausea during drug therapy. 5HT reuptake blockers are effective in treating depressive psychosis and in controlling appetite. The progress in the study of the role the 5HT systems in brain function has relied considerably on techniques of radiolabelling the 5HT receptors using ligands of high specific radioactivity. However this technique for monitoring and/or visualizing brain 5HT receptors has limitations. Receptor adaptation involves changes in the levels of receptors, receptor mobility, and the interaction with other cellular constituents. These critical properties of receptors are best monitored using fluorescent probes, which are sensitive to the microenvironment of the receptor. In Phase I of the project we propose to synthesize fluorescent probes as a novel approach to monitor 5HT receptor mobility in brain membranes. Fluorescent compounds will be coupled to 5HT receptor agonists and antagonists. We will first test the affinity and selectivity of these compounds for multiple 5ht receptors. Neural membranes at various levels of tissue organization will be exposed to the fluorescent probe, photobleached by laser beam, and the recovery of fluorescence will be monitored by fluorescence microscopy.